This invention relates in general to robots for use in integrated circuit production and relates more particularly to a robot that is magnetically coupled to reduce particulate contamination within one or more process chambers.
Integrated circuit processing technology is continuously concerned with reducing the feature size of circuits to increase the amount of circuitry that can be packed onto an integrated circuit of a given size and to increase the speed of operation by reducing the distance that signals need to travel within such circuits. Particulates of diameter even several times smaller than the feature size of a component can cause failure of the IC if a particulate was present at a critical location in the IC during an important process step. This problem is particularly acute for large area ICs such as microprocessors and .gtoreq.4 megabit memories because such ICs have an increased area over which a critical defect can occur.
The multilayer structure of typical ICs also increases the effect of particulates on yield because a particulate incorporated into one level of an IC can affect not only the circuitry on that level, but also circuity on other levels. A defect in an embedded level of an IC can propagate through overlying layers, distorting the topography and thus disrupting operation of those circuit elements. For these reasons it is important to minimize the amount of particulates that come into contact with a wafer immediately before and during processing.
FIG. 1 illustrates common particulates and particulate sizes that are present in the ambient atmosphere. Expensive, intricate clean rooms and clean room procedures are utilized to significantly reduce the amount of airborne particulates to which a wafer is exposed during IC fabrication. Unfortunately, clean rooms cannot prevent particulates from being produced within an integrated circuit fabrication system.
FIG. 2 illustrates an existing wafer handling system 20 that allows a robot 21 to supply wafers to any of a plurality of IC processing chambers. Robot 21 includes an extensible arm 28 that can extend a wafer blade 29 radially into any of chambers 23-27. Arm 28 is mounted on a rotatable table 210 that enables the extensible arm to be directed at any selected one of chambers 23-27. A vacuum is maintained in chamber 211 containing the robot so that the chambers 24-27 and 211 can be carefully cleaned and purged before wafers are introduced for processing. This system enables wafers 22 to be exchanged between a wafer cassette elevator 23 and any of the chambers 24-27 without breaking vacuum in these chambers. Unfortunately, the mechanical steps of moving wafers among the chambers and from the wafer cassette elevator 21 to the chambers and back produces some particulates that can contaminate the wafers. It is therefore important to minimize the amount of particulate production by such a robot.
Rotatable table 210 and robot 21 are each coupled to motors exterior to chamber 211 to prevent wafers from being contaminated by operation of such motors. These motors are typically in an atmospheric environment, so rotary seals are required to separate chamber 211 from the environment in which the motors are contained. These seals enable the motor shafts to extend between the motor and robot chambers while preserving the pressure difference between these chambers. Tests have shown that these rotary seals are a major source of particulate generation within chamber 211.
In a robot system manufactured by Anelva, these rotary seals are replaced by a magnetic coupler 30 illustrated in FIG. 3. Coupler 30 consists of an outer assembly 31, a vacuum assembly 38 and an inner assembly 313.
Outer assembly 31 includes a cylindrical casing 32, a bottom cap 33 and a top cap 34. Casing 32 encloses a chamber 35 and has attached to its inner wall a set of six bar magnets 36 polarized in the radial direction of casing 32. Bottom cap 33 includes a ball bearing ring 37 into which can be fitted vacuum assembly 38.
Vacuum assembly 38 includes a flange 39 and a cylindrical shell 310 enclosing an inner cavity 311. In an integrated circuit processing system utilizing a robot such as that shown in FIG. 2, wall 40 (see FIG. 4) between chamber 41 containing motor 42 and chamber 211 containing the robot contains a hole of diameter slightly larger than the outer diameter of cylindrical shell 310. A vacuum ring 43 (see FIG. 4) is slipped over cylindrical shell 310 which is then inserted through this hole in the wall and attached to the wall by flange bolts through flange 39 with sufficient pressure against the vacuum ring to maintain the pressure difference between the motor and robot chambers.
Inner assembly 313 includes a ferrite inner pole section 314 having a set of six poles 315. On one end of section 314 is a ball bearing ring 316 and on the other end is a shaft 317 over which is slipped a ball bearing ring 318. When this inner assembly is inserted into inner cavity 311, ball bearing rings 316 and 318 cooperate to center shaft 317 and inner pole section 314 within cavity 311 and to enable inner pole section 314 and shaft 317 to rotate easily within this cavity. Shaft 317 is then connected to the robot to activate various operations of that robot.
Outer assembly 31 is slipped over shell 310 until shell 310 fits into ball bearing ring 37. Ball bearing rings 37, 316 and 318 enable both inner assembly 313 and outer assembly 31 to rotate relative to vacuum assembly 38. A motor is connected to outer assembly 31 to controllably rotate that assembly relative to the vacuum assembly. Pole magnets 36 within outer assembly 36 each magnetically couple to an associated pole 315 of ferrite inner pole section 314 so that the inner assembly rotates with the outer assembly.
This magnetic coupler enables elimination of the rotary seals, but exhibits several deficiencies. First, the magnetic coupler should allow more than one rotatable axis to penetrate through the wall between the motor and robot chambers so that more than one degree of motion can be imported by the motor section to the robot. Second, the magnetic coupling between the outer and inner assemblies should be stronger. Third, the structure of the coupling should be such that the vertical position of the robot does not vary when a vacuum is established in the robot chamber. Such variation could produce misalignment of a robot blade with a wafer in a chamber external to chamber 211.